Something

<?php

if($_POST['action'] == 'signup') {

  $list = $_POST['list'];
  $email = $_POST['email'];
  
  add_to_list($email, $list);
  
  if($_POST['ajax'] == 'true') {
   echo 'ok'; die();
  } else {
    $return_url = $_POST['return_url'];
    header("Location: $return_url".'?signedup');
  }
}

function add_to_list($email, $list) {
	include('../includes/db.php');
	$db_name = 'announce_list';
	$date = $db->escape(date("F j, g:i a T"));
	$query = "INSERT INTO $db_name (`email`, `list`, `date`) VALUES('$email', '$list', '$date')";
	$db->query($query);
}

?>